Yushin V.V.1, Afanasiev-Grigoriev A.G.1, Malakhov V.V.2 2014. The male gonad of the marine nematode Enoplus: No single distal tip cell but multiple uniform epithelial cells // Invertebrate Zoology. Vol.11. No.2: 361–372 [in English].

1 A.V. Zhirmunsky Institute of Marine Biology FEB RAS, Palchevskogo Str., 17, Vladivostok 690041, Russia, e-mail: vvyushin@yandex.ru

2 Department of Invertebrate Zoology, Biological Faculty, M.V. Lomonosov Moscow State University, Leninskie Gory, Moscow, 119991, Russia.

ABSTRACT: The distal tip cell (DTC) is a large single cell located at the apex of nematode gonadal arms. It is well investigated in Caenorhabditis elegans Maupas, 1900 and described in many other species of class Chromadorea. It has been obtained convincing evidence that in C. elegans the DTC plays an essential role in the development of the gonads and regulation of gametogenesis. We have studied the fine structure of the distal part of the testis in free living marine nematodes Enoplus. TEM observations revealed the absence of a large specialized DTC at the apex of testes in E. michaelseni (Linstow, 1896) and E. brevis Bastian, 1865. The testis of both species is lined with numerous uniform testis epithelial cells (TEC) forming an uninterrupted epithelium adjacent to the basal lamina. Besides that, TEC form long outgrowths protruding deeply into the testis between spermatogonia. Unlike a single DTC of C. elegans, the multiple TEC in Enoplus spp. show hardly any signs of synthetic activity. They possess neither nucleoli nor a rough endoplasmic reticulum in their cytoplasm, but contain thick bundles of filaments giving no evidence for a glandular or a hormonal function. The multicellular epithelium of the distal part of the testis in Enoplus spp. complements other plesiomorphic characters of enoplid structure and development (e.g. indeterminate early development, absence of cell constancy, regeneration ability, preservation of the nuclear envelope in spermatozoa) and may be considered as additional evidence for the basal position of the order Enoplida within the phylum Nematoda.

KEY WORDS: Caenorhabditis elegans, distal tip cell, DTC, Enoplida, Enoplus brevis, Enoplus michaelseni, free-living marine nematodes, gametogenesis, testis.

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